Electric control system



R. s. M FARLANE 2,158,135

ELECTRIC CONTROL SYSTEM May 16, 1939.

Filed NOV. 5, 1936 MOVING COIL 5M0, km 4M. M

Patented May 16,1939

PATN'E" orrics 14 Claims.

My invention relates, generally, to electric control systems and it has particular relation to the arrangement and construction of a system for controlling the resistance of a mass of material that is positioned between and heated by current flow from one or more pairs of electrodes.

In the copending application of Charles F. Ramseyer, Serial No. 67,863, filed March 9, 1936, and assigned to the assignee of this application, there is disclosed a method for making mineral wool from coal ashes that are obtained from coal fired boiler plants and the like, the disposal of which prior to this invention was an item of expense rather than of profit. According to the method disclosed in this copending application an electric furnace is provided for receiving the ash as it comes from the boiler plant for the purpose of controlling its temperature and viscosity in such manner as to facilitate the subsequent blowing of this product into mineral wool by steam issuing from a Jet under high pressure. In order to satisfactorily carry out this process it is essential that the viscosity of the molten ash product be held substantially constant so that a uniform product will result when it is subjected to the action of the steam jet. As indicated in this copending application the resistance of the molten mass decreases with an increase in temperature. A change in the resistance is accompanied by a change in the viscosity of the molten mass and, therefore, its resistance is an indication of the viscosity so that, if the resistance is held constant, the viscosity will also be held constant.

It has been found desirable to maintain the resistance of the molten mass of material within very close limits. A change of one percent in the resistance of the molten mass of material will produce a considerable effect on the resulting product. The furnace that is used comprises a plurality of pairs of electrodes that are individually energized by alternating current from a common source. When such an arrangement is employed, it has heretofore been difficult to so regulate the voltage that is applied to each pair of electrodes in such manner as to maintain the resistance of the mass of material therebetween within the required limits to provide the required viscosity of the material as it is subjected to the action of the steam jet.

Therefore, the object of my invention, as here in disclosed, generally stated is to provide a system for controlling the resistance of a mass of molten material that will be simple, efiicient and accurate in operation and which may be readily and economically manufactured and installed.

The principal object of my invention is to provide for maintaining the resistance of a mass of material that is heated by current flow therethrough substantially constant.

An important object of my invention is to pro vide for individually adjusting the voltage that is maintained between the various electrodes, energized from a common source, that are employed to heat a mass of material positioned therebetween.

A specific object of my invention is to balance the total current supplied to the various electrodes against the voltages applied thereto and to utilize the difference between these effects to control the applied voltage in such manner as to maintain the resistance of the mass of molten material substantially constant.

Another specific object of my invention is to provide a control device for effecting the foregoing objects that will be highly sensitive to slight changes in the resistance of the mass of material but which will not be damaged on the occurence 01' wide variations in this resistance. I

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

My invention, accordingly, is disclosed in the embodiment hereof shown in the accompanying drawing, and it comprises the features of construction, the combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the application of. which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawing in which the single figure illustrates, diagrammatlcally, a concrete embodiment of my invention.

As indicated hereinbefore, an electric furnace is employed for maintaining the desired viscosity of the molten ash as it is received from the boiler and before it is subjected to the action of the steam jet. This furnace comprises a plurality of oppositely disposed-electrodes that are arranged to be independently energized from a source of alternating current. Since the resistance of the mass of material is a function of the current flowing to the electrodes and the voltage applied thereto, a device that will measure these quantitles and correlate them may be employed to provide an indication of the resistance of the mass of material and to comprise the control element for regulating the voltage that is obtained from the alternating current source in such manner as to maintain this resistance substantially constant.

For this purpose I have provided a balancing transformer that comprises a core structure having a central leg on which windings, that are connected to be responsive to the current flowing to and the voltage applied across the electrodes of the furnace, may be positioned. These windings are so connected that no flux is present in the leg on which they are disposed when the resistance, and thus the viscosity, of the mass of material in the furnace is maintained at the desired value. An exploring winding is positioned on this leg and it will have a voltage induced therein that will be proportional in phase and magnitude to the resultant flux in the legthat is generated by the combined action of the current and voltage windings. The exploring winding is connected to energize the moving coil of an electrodynamometer contact making device, the fixed coil of which is energized from the alternating current source that also is connected to supply power for operating the furnace. The contact mechanism is connected to control the functioning of a voltage regulator interposed in the power circuit and the voltage that is applied is raised or lowered as required.

Referring now particularly to the single figure shown in the drawing, it will be observed that the reference character In designates a source of alternating current, such as a sixty cycle source. The generator i0 is connected to energize a furnace, shown generally at H, through transformers shown generally at I 2 and i3. These transformers are provided, respectively, with primary windings i 4 and ii that are connected in series circuit relation and to the source i0 and with secondary windings l8 and I! that are connected to energize the electrodes I 3 and I3 respectively in the furnace Ii.

' It will be understood that the furnace II has positioned therein the molten mass of material M in the form of coalash that is obtained in this state from the coal fired boiler. The temperature of the material M is maintained at the desired point by current flow from the pairs of electrodes i 8 and I9. Since the resistance of the material M varies inversely with the current flow therethrough, there is a tendency for the entire current flow to concentrate between one pair of electrodes when equal voltages are applied to both pairs. It is desirable to maintain a uniform distribution of current flow from each pair of electrodes and for this purpose the primary windings l4 and I5 are connected in series circuit relation, while the secondary windings i8 and I! are connected to individually energize the various pairs of electrodes i8 and I9. It will be understood, of course, that a larger number of pairs of electrodes may be employed, but for illustrative purposes only two pairs have been shown. This particular arrangement and connection for the transformers l2 and i3 are described in detail and claimed in my copending application, Serial No. 121,090 filed January 18, 1937, and assigned to the assignee of this application.

The voltage that is available for operating the furnace ll may be controlled by a Voltage regulator, shown generally at 20, and interposed between the source IO and the series connected primary windings i4 and I6. The voltage regulator 20 may be of any suitable commercial type and preferably it is provided with a moving coil 20M that is rotated with respect to a stationary coil 238 by a reversible series motor, shown generally at 2!. The motor 2| is provided with an armature 22 which is mechanicallyconnected to the moving coil 20M and two series field windings 23 and' 24, the energization of which is selectively controlled by a raise relay, shown generally at 26, and a lower relay, shown generally at 28. These relays are provided with make contact members 23a and 23a and with operating windings 25w and 28w. The motor 2| and the relays 2-5 and 28 may be connected for energization to the secondary winding 2'! of a. transformer, shown generally at 28, the primary winding 28 of which is connected for energization to the alternating current source ill. It will be understood, on energization of the operating winding 25w of the raise relay 25, the series field winding 23 will be connected in series circuit relation with the armature 22 to operate the moving coil 20M of the voltage regulator 20 in such a direction as to raise the voltage that is applied to the transformers i2 and i3. Likewise, when the lower relay. 28 is operated, the series field winding 24 will be energized in series circuit relation with the armature 22 to eifect the rotation of the latter in the opposite direction and to move the moving coil 20M of the voltage regulator 20 in a corresponding direction to lower the applied voltage.

As has been set forth hereinbefore, the resistance of the material M in the furnace Ii is a function of the current flowing to the pairs of electrodes i3 and I9 and the voltages that are applied thereto. Accordingly, I have provided for measuring and comparing these two quantities for the purpose of obtaining still another quantity which will be a function of these two and which may be employed for controlling the functioning of the relays 25 and 28 in accordance therewith. r

For this purpose a balancing transformer, shown generally at is provided. The balancing transformer 35 is provided with a core structure 36 that is-rectangular in shape and substantially uniform in cross-section. A central leg 31 is provided in the core structure 38 and at its middle section it is provided with a reduced or saturation portion 33, the function of which will be set forth hereinafter. The currents flow to both pairs of electrodes l3 and I9 is totalized by a winding 33 of a current transformer which, as illustrated, surrounds one conductor of each circuit that is connected to the secondary windings i6 and H. The winding 39 of the current transformer is connected to energize a current winding comprising sections 40 and 4| that are disposed uniformly on opposite sides of the reduced or saturation portion 33 of the leg 31. The voltage that is applied across the electrodes i3 is measured by a voltage winding 42, that is positioned on the leg 31 on one side of the saturation portion 33. The voltage winding 42 is energized through an adjustable resistor 43. In like manner the voltage that is applied to the electrodes i9 is measured by a voltage winding 44 that is positioned on the leg 31 and on the right hand side of the saturation portion 38. The voltage winding 44 is energized through an adjustable resistor 45.

It will be obvious that a current transformer individual to each of the secondary windings i6 and I1 may be provided instead of the single current transformer with the winding 39 that itself totalizes the total current flowing. The second ary windings of these transformers should then be connected to energize individual current windings on the leg 31.

In like manner individual 76 potential transformers may be provided having primary windings connected. to each of the pairs of electrodes I8 and 9 and the secondary windings connected in series circuit relation and to a single winding on the leg 31. However, it is undesirable to use these various transformer arrangements since it is not practical to construct a transformer that has uniform regulation from no load to full load operating conditions.

Instead of using a voltage winding on the leg 3'! for each of the pairs of electrodes, a single winding may be provided and connected across that part of the furnace H, which operating experience indicates is subjected to a voltage that is the average of the voltages applied to the various pair of electrodes. In such case this winding should be uniformly distributed on opposite sides of the saturation portion 38.

The current and voltage windings on the leg 31 are so connected that the fluxes generated thereby will be in opposition to each other. That is, the flux that is generated by the sections 40 and 4| of the current winding will oppose the flux that is generated by the voltage windings 42 and 44. The resultant flux is measured by an exploring winding 46 which is positioned on the saturation portion 38, as illustrated. The phase of the voltage that is induced in the exploring winding 46 will depend upon the phase of the resultant flux that is generated in the leg 31 by the current and voltage windings. Thus, if the flux generated by the current winding predominates, the voltage induced in the exploring winding 46 will be in one direction. Likewise, if the flux generated by the voltage windings 42 and 44 predominates. the voltage that is induced in the exploring winding 46 will be in the opposite direction.

In order to obtain a high degree of sensitivity. it is necessary to induce a relatively high voltage in the exploring winding 46 for a small difference between the fluxes generated by the current and voltage windings. When the exploring winding 46 is arranged to be sensitive to slight changes. a destructive voltage may be induced therein on the occurrence of large differences inthe fluxes generated by the current and voltage windings. It is to avoid this possibility while still retaining the high degree of sensitivity that the exploring winding 46 is positioned on the saturation portion .38 of the leg 31. The portion 38 is so designed that it will saturate on the occurrence of a predetermined difference in the fluxes generated by the current and voltage windings. It will now be apparent that the voltage that is in duced in the exploring winding 46 is limited by this saturation feature and, therefore, a destructive voltage will not be induced therein. Furthermore, because of the positioning of the exploring winding 46 on the reduced or saturation portion 38, its turns do not link the leakage flux from the current and voltage windings.

The voltage that is generated in the exploring winding 46 is measured by a moving coil 4'! of a contact making electro-dynamometer, shown generally at 48. A fixed coil 49 is provided in the usual manner and is connected for energization across the secondary winding 2! of the trans former 28. The moving coil 41 rotates about a pivot point 50 and carries therewith a movable contact member 5| that is arranged to engage either of stationary contact members 52 or 53 dedepending upon the direction in which the moving coil 41 rotates. This direction of rotation depends upon the phase relationship between the voltage that is applied to the moving coil 41 and the energizing voltage of the fixed coil 49. It will be understood that this phase relationship will be controlled by the resultant flux from the current and voltage windings on the balancing transformer 35 and the voltage induced thereby in the exploring winding 46.

It may be desirable to provide slightly different effects in the balancing transformer 35 from the voltages between the pairs of electrodes I8 and I9. It is for this purpose that the adjustable resistors 43 and 45 are provided and connected in series circuit relation with the voltage windings 42 and 44 respectively. Since only the resultant effect of the fluxes generated by the voltage windings 42 and 44 controls the voltage that is induced in the exploring winding 46 in conjunction with the sections 40 and 4| of the current winding, it will be obvious that different effects may be obtained from the different pairs of electrodes. Such operation is desirable since the heating characteristics in different parts of the furnace may vary because of construction features and for other reasons. Ordinarily the resistors 43 and 45 will be gang operated so that only a single adjustment is required to change the resistance of the mass of material M in the furnace II from one value to another.

In operation it will be assumed that the adjustable resistors 43 and 45 have been preset as determined by previous calibration to maintain the desired resistance between the electrodes i8 and I9. Assuming that the current flowing to the electrodes |8, |9 as totalized by the winding 39 and the sections 40 and 4| of the current winding is sufficient to generate a flux in the leg 31 that exceeds the flux generated by the voltage windings 42 and 44, the moving coil 41 will be operated in such direction as to cause the movable contact member 5| to engage the stationary contact member 52 and to energize the operating winding 26w of the lower relay 26. The motor 2| is then energized in such direction as to operate the voltage regulator 20 to reduce the voltage that is applied to the transformers l2 and I3. If the reverse condition prevails, the moving coil 4! will be rotated in the opposite direction, causing the contact member 5| to engage the stationary contact member 53 and to energize the operating winding 2510 of the raise relay 25. The motor 2| will then be energized to operate the voltage regulator 20 in such direction as to raise the voltage that is applied to the transformers l2 and I3, In this manner the voltage that is applied to the furnace Ii is adjusted as desired by the combined action of the current and voltage windings on the bal ancing transformer 35 to maintain the resistance and consequently the viscosity of the material M in the furnace H at a substantially constant value.

It will be obvious that further changes may be made in the above construction and different embodiments of the invention may be made without departing from the scope thereof. Therefore, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense,

I claim as my invention:

1. Apparatus for controlling the resistance of a mass of material heated by current flow from a plurality of pairs of electrodes comprising, in combination, means for individually energizing said pairs of electrodes, means for totalizing the current flow to said pairs of electrodes, means for totalizing the voltages applied to said pairs of electrodes, and means arranged and adapted to be responsive to the combined effect of said totalizlug means for regulating the voltage applied to said pairs of electrodes.

2. Apparatus for controlling the resistance of a mass of material heated by current flow from a plurality of pairs of electrodes comprising, in combination, means for individually energizing said pairs of electrodes, means for totalizing the current flow to said pairs of electrodes, means for totalizing the voltages applied to said pairs of electrodes, means for adjusting one of said totalizing means to maintain different values of resistance, and means arranged and adapted to be responsive to the combined effect of said totalizing means for regulating the voltage applied to said pairs of electrodes.

3. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, means for totalizing the current flow to each pair of electrodes, means for totalizing the voltages applied across said pairs of electrodes, and means arranged and adapted to be responsive to the combined effect of. both said totalizing means for controlling the voltage from said source in such manner as to maintain the resistance of said mass of material substantially constant.

4. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, means for totalizing the current flow to each pair of electrodes, means for totalizing the voltages applied across said pairs of electrodes, means for individually adjusting the totalizing means of each pair of electrodes to adjust for different voltages between said pairs of electrodes, and means arranged and adapted to be responsive to the combined effect of both said totalizing means for controlling the voltage from i said source in such manner as to maintain the resistance of said mass of material substantially constant.

5. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes comprising, in combination, a plurality of transformers having primary windings connected in series circuit relation for energization to an alternating current source and secondary windings connected to individually energize each pair of electrodes, means for totalizing the current flow to each pair of electrodes, means for totalizing the voltages applied across said pairs of electrodes, and means arranged and adapted to be responsive to the combined effect of both said totalizing means for controlling the voltage applied to said series connected primary windings from said source in such manner as to maintain the resistance of said mass of material substantially constant.

6. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a pair of electrodes comprising, in combination, circuit means for connecting said electrodes for energization to an alternating current source, an electric trans- -voltage induced in said former having a stationary core, a current winding on said core connected to be responsive to theerate flux in said core in a direction opposite to the flux generated therein by said current winding, and means arranged and adapted to be re sponsive to the resultant flux generated by said current and voltage windings in said transformer for regulating the voltage applied to said electrodes in such manner as to maintain the resistance of said mass of material therebetween substantially constant.

7. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, a balancing transformer, a current winding in said transformer, means for connecting said current winding to be responsive to the total current flow to said electrodes, a plurality of voltage windings in said transformer, means for individually connecting said voltage windings to be responsive to the individual voltages applied across each pair of electrodes, and means arranged and adapted to be responsive to the combined effect of said current and voltage windings in said transformer for regulating the voltage from said source in such manner as to maintain the resistance of said mass of material substantially constant.

8. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, a balancing transformer, a current winding in said transformer, means for connecting said current winding to be responsive to the total current flow to said electrodes, a plurality of voltage windings in said transformer,

means for individually connecting said voltage windings to be responsive to the individual voltages applied across each pair of electrodes, ad- Justable impedance means individual-- to each of said voltage windings for adjusting for different voltages between said pairs of electrodes, and means arranged and adapted to be responsive to the combined effect of said current and voltage windings in said transformer for regulating the voltage from said source in such manner as to maintain the resistance of said mass of material substantially constant.

9. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, a transformer core having a central leg, a current winding on said leg connected to be responsive to the total current flow to said electrodes, a plurality of voltage windings on said leg connected individually across each pair of electrodes, an exploring winding on said leg having a voltage induced therein corresponding in phase and magnitude to the resultant flux generated by said current and voltage windings, means for varying the voltage applied to said first named means, and means responsive to the exploring winding for controlling said voltage varying means in such manner as to maintain the resistance of said material substantially constant.

10. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, a transformer core having a central leg, a current winding on said leg connected to be responsive to the total current flow to said electrodes, a plurality of voltage windings on said leg connected individually across each pair of electrodes, adjustable resistance means connected in series circuit relation with each of said voltage windings for adjusting for different voltages between said pairs of electrodes, an exploring winding on said leg having a voltage induced therein corresponding in phase and magnitude to the resultant flux generated by said current and voltage windings, means for varying the voltage applied to said first named means, and means responsive to the voltage induced in said exploring winding for controlling said voltage varying means in such manner as to maintain the resistance of said material substantially constant.

11. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said current source, a balancing transformer having a closed core structure of substantially uniform cross-section, a central leg in said core structure having a reduced saturation portion, a current winding on said leg disposed uniformly on opposite sides of said saturation portion and connected to be responsive to the total current flow-to said electrodes, a plurality of voltage windings on said leg disposed uniformly on opposite sides of said-saturation portion and connected individually across each pair of electrodes, an exploring winding on said saturation portion having a voltage induced therein corresponding in phase and magnitude to the resultant flux generated by said current and voltage windings, a voltage regulator connected to control the voltage applied tosaid first named means, and means responsive to the voltage induced in said exploring winding and connected to control said voltage regulator in such manner as to maintain the resistance of said material substantially constant.

12. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes energized from an alternating current source comprising, in combination, means for individually energizing each pair of electrodes from said currentsource, a balancing transformer having a closed core structure of substantially uniform cross-section, a central leg in said core structure having a reduced saturation portion, a current winding on said leg disposed uniformly on opposite sides of said saturation portion and connected tobe responsive to the total current flow to said electrodes. a plurality of voltage windings on said leg disposed uniformly on opposite sides of said saturation portion and connected individually across each pair of electrodes, adjustable resistance means connected in series circuit relation with each of said voltage windings for adlusting for different voltages between said pairs of electrodes, an exploring winding on said saturation portion having a voltage induced therein corresponding in phase and magnitude to the resultant flux generated by said current and voltage windings, a voltage regulator connected to control the voltage applied to said first named means, and means responsive to the voltage induced in said exploring winding and connected to control said voltage regulator in such manner as to maintain the resistance of said material sub stantially constant.

13. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a plurality of pairs of electrodes comprising, in combination, a plurality of transformers having primary windings connected in series circuit relation for energization to an alternating current source and secondary windings connected to individually energize each pair of electrodes, a balancing transformer having a closed core structure of substantially uniform cross-section, a central leg in said core structure having a centrally located reduced saturation portion, a current winding connected to be responsive to the total current flow to said electrodes and disposed uniformly on said leg on opposite sides of said saturation portion, a plurality of voltage windings connected individually across each pair of electrodes and disposed uniformly on said leg on opposite sides of said saturation portion in such manner relative to said current winding as to generate flux in said leg in opposition to the flux generated by said current winding, an exploring winding on said saturation portion having a voltage induced therein corresponding in phase and magnitude to the resultant flux generated by said current and voltage windings, a voltage regulator connected to control the voltage applied to said series connected primary windings, relay means connected to efiect the operation of said voltage regulator in opposite directions,a moving coil connected for energization to said exploringwinding, contact means operated by said moving coil and connected to control said relay means, and a fixed coil connected for energization to said alternating current source and cooperating with said moving coil.

14. Apparatus for controlling the resistance of a mass of material positioned between and heated by current flow from a pair of electrodes comprising, in combination, circuit means for connecting said electrodes for energization to an alternating current source, a balancing transformer, a current winding in said transformer, connected to be responsive to the current flow to said electrodes, a voltage winding in said transformer connected to be responsive to the voltage applied acme said electrodes, an exploring winding in said transformer inductively related to said current and voltage windings for obtaining a resultant voltage that is a function of the current in and the voltage across said circuit means. and means arranged and adapted to be responsive to said resultant voltage for regulating the voltage applied to said electrodes in such manner as to maintain the resistance of said mass of material therebetween substantially constant.

RAYMOND S. MACFARLANE. 

